Liquid fluoropolymer composition and process for producing crosslinked fluorochemical

ABSTRACT

It is an object of the present invention to provide a liquid composition which comprises an acid/acid salt group-containing polymer and from which cured articles excellent in mechanical characteristics and undergoing only slight dimensional changes depending on the moisture content can be produced by application thereof to a substrate or impregnation of a porous material therewith. The present invention relates to a fluoropolymer liquid composition comprising a fluoropolymer liquid (A) which comprises a liquid medium and a crosslinkable functional group-containing crosslinkable fluoropolymer, wherein said fluoropolymer liquid (A) is a fluoropolymer liquid dispersion (AD) having, dispersed in a liquid dispersion medium, particles of a crosslinkable fluoropolymer (PD) containing acid/acid salt groups or organic groups capable of undergoing hydrolysis and thus being converted to carboxyl groups, or a fluoropolymer solution (AS) having, dissolved in a fluorosolvent or an alcohol/water mixed solvent, a crosslinkable fluoropolymer (PS) containing acid/acid salt groups or acid/acid salt groups precursors; 
         said acid/acid salt groups are sulfonic acid groups, carboxyl groups or groups of the formula —SO 2 NR 2 R 3 , —SO 3 NR 4 R 5 R 6 R 7 , —SO 3 M 1   1/L , —COONR 8 R 9 R 10 R 11  or —COOM 2   1/L , wherein R 2  represents a hydrogen atom or M 5   1/L , R 3  represents an alkyl group or an sulfonyl-containing group, R 4 , R 5 , R 6 , R 7 , R 8 , R 9 , R 10  and R 11  are the same or different and each represents a hydrogen atom or an alkyl group, and M 1 , M 2  and M 5  each represents a metal having a valence of L, said metal having a valence of L being a metal belonging to the group 1, 2, 4, 8, 11, 12 or 13 of the periodic table; and    said acid/acid salt groups precursors are —SO 2 F, —SO 2 NR 22 R 23  (wherein R 22  and R 23  are the same or different and each represents an alkyl group) or organic groups capable of undergoing hydrolysis and thus being converted to carboxyl groups.

TECHNICAL FIELD

This invention relates to a fluoropolymer liquid composition and to amethod of producing a fluorine-containing cured article.

BACKGROUND ART

Fluorine-containing electrolyte membranes are mainly used in solidpolymer fuel cells currently attracting attention. However, they haveproblems. For improving the power generating characteristics of fuelcells, such means is available as increasing the ion exchange capacityof the electrolyte membrane or diminishing the membrane thickness, forinstance. In either case, however, decreases in mechanical strength willsurely result. Since the membrane is firmly compressed during use, themembrane undergoes deformation and degradation due to the creepphenomenon, or is deteriorated due to repeated expansion and shrinkageon the occasions of starting and stopping power generation and, inextreme cases, pinholes are made, allowing mixing of hydrogen and oxygenwith each other.

For preventing fluorine-containing electrolyte membranes from beingdeteriorated, it has been proposed that the electrolyte membranes becrosslinked and thus converted to cured membranes (cf. e.g. PatentDocument 1: Japanese Kokai Publication S60-133031; Patent Document 2:Japanese Kokai Publication S54-107889; Patent Document 3: Japanese KokaiPublication S54-52690; Patent Document 4: Japanese Kokai PublicationS61-276828; Patent Document 5: Japanese Kokai Publication 2000-188013;Patent Document 6: Japanese Kokai Publication 2002-53619; PatentDocument 7: Japanese Kokai Publication 2003-128833). As for the methodof obtaining cured membranes, a method is known which comprises blendinga resin with a crosslinking agent and subjecting the mixture toextrusion molding. However, there are problems; the crosslinkingreaction already occurs in the molding machine and, therefore, it isdifficult to control the crosslinking reaction, hence it is difficult tomanufacture membranes constant in quality.

Also known as a method of producing fluorine-containing curedelectrolyte membranes is the method comprising blending a resin with acrosslinking agent and subjecting the mixture to hot press molding (cf.e.g. Patent Document 6). However, this method has a problem: it isdifficult to obtain membranes large in size, so that batch production isunavoidable and mass production is difficult to make.

Another known method of producing fluorine-containing cured electrolytemembranes comprises impregnating perfluoro type sulfonyl fluoridemembranes made in the conventional manner with a crosslinking agent andcuring them by heating or exposure to high energy radiation (cf. e.g.Patent Document 5). However, this document does not disclose thecrosslinking of cast membranes formed from a solution, following byheating, for instance. Further, the crosslinking agent is generally alarge molecule and it is difficult for that agent to uniformly penetrateinto the membranes; it is a problem that uniformly cured membranes arethus difficult to obtain.

A further known method of producing fluorine-containing curedelectrolyte membranes comprises blending a ˜SO₂F type dispersion with acrosslinking agent and, after membrane formation by casting, curing themembranes by heating (cf. e.g. Patent Document 7). However, the ˜SO₂Ftype dispersion contains the emulsifier and/or initiator residue, whichproduces a problem, namely deteriorates the characteristics of themembranes obtained.

DISCLOSURE OF INVENTION Problems which the Invention is to Solve

In view of the above-discussed state of the art, it is an object of thepresent invention to provide a liquid composition which comprises anacid/acid salt group-containing polymer and from which cured articlesexcellent in mechanical characteristics and undergoing only slightdimensional changes depending on the moisture content can be produced byapplication thereof to a substrate or impregnation of a porous materialtherewith.

Means for Solving the Problems

The present invention relates to a fluoropolymer liquid compositioncomprising a fluoropolymer liquid (A) which comprises a liquid mediumand a crosslinkable functional group-containing crosslinkablefluoropolymer, wherein said fluoropolymer liquid (A) is a fluoropolymerliquid dispersion (AD) having, dispersed in a liquid dispersion medium,particles of a crosslinkable fluoropolymer (PD) containing acid/acidsalt groups or organic groups capable of undergoing hydrolysis and thusbeing converted to carboxyl groups, or a fluoropolymer solution (AS)having, dissolved in a fluorosolvent or an alcohol/water mixed solvent,a crosslinkable fluoropolymer (PS) containing acid/acid salt groups oracid/acid salt groups precursors;

said acid/acid salt groups are sulfonic acid groups, carboxyl groups orgroups of the formula —SO₂NR²R³, —SO₃NR⁴R⁵R⁶R⁷, —SO₃M¹ _(1/L),—COONR⁸R⁹R¹⁰R¹¹ or —COOM² _(1/L), wherein R² represents a hydrogen atomor M⁵ _(1/L), R³ represents an alkyl group or an sulfonyl-containinggroup, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰ and R¹¹ are the same or different andeach represents a hydrogen atom or an alkyl group, and M¹, M² and M⁵each represents a metal having a valence of L, said metal having avalence of L being a metal belonging to the group 1, 2, 4, 8, 11, 12 or13 of the periodic table; and said acid/acid salt groups precursors are—SO₂F, —SO₂NR²²R²³ (wherein R²² and R²³ are the same or different andeach represents an alkyl group) or organic groups capable of undergoinghydrolysis and thus being converted to carboxyl groups.

The present invention relates to a method of producing afluorine-containing cured article,

in which the fluoropolymer liquid composition mentioned above is appliedto a substrate or a porous material is immersed in said composition, theliquid medium is then removed and a crosslinking treatment is carriedout to produce said fluorine-containing cured article.

The present invention relates to a method of producing afluorine-containing cured article,

in which the fluoropolymer liquid composition mentioned above is appliedto a substrate or a porous material is immersed in said composition, theliquid medium is then removed and a crosslinking treatment is carriedout using a peroxide compound as a crosslinking reaction initiator toproduce said fluorine-containing cured article.

In the later method of producing a fluorine-containing cured article,the fluoropolymer liquid composition to be used may be one in which thecrosslinkable functional group is —I or —Br and a polyfunctionalunsaturated compound is contained as the crosslinking agent (B).

In the following, the present invention is described in detail.

The fluoropolymer liquid composition of the invention comprises afluoropolymer liquid (A), which in turn comprises a liquid medium and acrosslinkable functional group-containing crosslinkable fluoropolymer.

The liquid medium is one of the liquid dispersion medium described laterherein, or a fluorosolvent or an alcohol/water mixed solvent.

The fluoropolymer liquid (A) is a fluoropolymer liquid dispersion (AD)having, dispersed in a liquid dispersion medium, particles of acrosslinkable fluoropolymer (PD) containing acid/acid salt groups ororganic groups capable of undergoing hydrolysis and thus being convertedto carboxyl groups, or a fluoropolymer solution (AS) having, dissolvedin a fluorosolvent or an alcohol/water mixed solvent, a crosslinkablefluoropolymer (PS) containing acid/acid salt groups or acid/acid saltgroups precursors.

The acid/acid salt groups are sulfonic acid groups, carboxyl groups oracid groups of the formula —SO₂NHR³ (wherein R³ represents an alkylgroup or a sulfonyl-containing group), or acid salts groups of theformula —SO₃NR⁴R⁵R⁶R⁷, —SO₃M¹ _(1/L), —SO₂NM⁵ _(1/L)R³, —COONR⁸R⁹R¹⁰R¹¹or —COOM² _(1/L) (wherein R³ is as defined above, R⁴, R⁵, R⁶, R⁷, R⁸,R⁹, R¹⁰ and R¹¹ are the same or different and each represents a hydrogenatom or an alkyl group, and M¹, M² and M⁵ each represents a metal havinga valence of L; said metal having a valence of L is a metal belonging tothe group 1, 2, 4, 8, 11, 12 or 13 of the periodic table). The acid/acidsalt groups precursors include —SO₂F, —SO₂NR²²R²³ (wherein R²² and R²³are the same or different and each represents an alkyl group; R²³ may be—R²⁸SO₂F or the like group mentioned later herein) or organic groupscapable of undergoing hydrolysis and thus being converted to carboxylgroups.

The sulfonyl-containing group represented by R³ is a sulfonylgroup-containing fluoroalkyl group and includes, among others,fluoroalkylsulfonyl groups which may terminally be substituted. As thefluoroalkylsulfonyl groups, there may be mentioned, for example,—SO₂R_(f) ⁶Z² groups (wherein R_(f) ⁶ represents a fluoroalkylene groupand Z² represents an organic group). As the organic group, there may bementioned, for example, —SO₂F, —SO₃H and —SO₃M¹ _(1/L), and these may beindefinitely repeated to give —SO₂(NR²⁷ SO₂R_(f) ⁶SO₂)_(k)NR²⁷SO₂—groups (wherein k represents an integer of not smaller than 1, R_(f) ⁶represents a fluoroalkylene group; R²⁷ represents an alkyl group, ahydrogen atom or a metal having a valence of L), for instance, or theorganic group may also be —SO₂(NR²⁷SO₂R_(f) ⁶SO₂)_(k)NR²⁷SO₂F,—SO₂(NR²⁷SO₂R_(f) ⁶SO₂)_(k)NR²⁷SO₃X (wherein k represents an integer notsmaller than 1 but not greater than 100, R²⁷ and R_(f) ⁶ are as definedabove and X represents a hydrogen atom or a metal having a valence ofL), or the like.

The organic groups capable of undergoing hydrolysis and thus beingconverted to carboxyl groups are preferably —COOR¹² (R¹² representing analkyl group) or —CONR²⁴R²⁵ (R²⁴ and R²⁵ being the same or different andeach representing an alkyl group or a hydrogen atom).

The alkyl group represented by R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹,R¹², R²², R²³, R²⁴, R²⁵ and/or R²⁷ includes alkyl groups containing 1 to4 carbon atoms such as methyl, ethyl, propyl and butyl. Among them,methyl or ethyl is preferred. The group R²³ may be, for example,—R²⁸SO₂F or such an indefinite repetition as —SO₂(NR²⁹SO₂R_(f)⁶SO₂)_(k)NR²⁹SO₂— (wherein k represents an integer of not smaller than1, R_(f) ⁶ represents a fluoroalkylene group, R²⁸ represents an alkylenegroup and R²⁹, like R²², represents an alkyl group), or—SO₂(NR²⁷SO₂R_(f) ⁶SO₂)_(k)NR²⁷SO₂F (wherein k represents an integer notsmaller than 1 but not greater than 100 and R²⁷ and R_(f) ⁶ are asdefined above).

The fluoropolymer liquid (A) is preferably a fluoropolymer liquiddispersion (AD) comprising a crosslinkable fluoropolymer (PD) containingcarboxyl groups, acid/acid salt groups or organic groups capable ofundergoing hydrolysis and thus being converted to carboxyl groups, or afluoropolymer solution (AS) comprising a crosslinkable fluoropolymer(PS) containing carboxyl groups, acid/acid salt groups or acid/acid saltgroups precursors. More preferably, it is a fluoropolymer liquiddispersion (AD) comprising a crosslinkable fluoropolymer (PD) containingacid salt groups, still more preferably a fluoropolymer aqueousdispersion (ADA) comprising a crosslinkable fluoropolymer (PD)containing —SO₃M¹ _(1/L) groups (M¹ being as defined above).

The above-mentioned acid/acid salt groups, the acid/acid salt groupsprecursors, and the organic groups capable of undergoing hydrolysis andthus being converted to carboxyl groups are each bound to a fluoroetherside chain represented by the general formula (I):—O—(CF₂CFY¹—O)_(n)—(CFY²)_(m)—  (I)wherein Y¹ represents a fluorine or chlorine atom or a perfluoroalkylgroup, n represents an integer of 0 to 3, the n atoms/groups of Y¹ maybe the same or different, Y² represents a fluorine or chlorine atom, mrepresents an integer of 1 to 5, and the m atoms of Y² may be the sameor different. The fluoroether side chain is preferably bound, via etherbonding, to a carbon atom constituting a perfluoroethylene unit in themain chain of the crosslinkable fluoropolymer. The perfluoroalkyl groupmentioned above preferably contains 1 to 3 carbon atoms.

The crosslinkable fluoropolymer is preferably a fluoropolymer precursorobtained by polymerizing a fluorovinyl ether derivative represented bythe general formula (II):CF₂═CF—O—(CF₂CFY¹—O)_(n)—(CFY²)_(m)-A   (II)wherein Y¹ represents a fluorine or chlorine atom or a perfluoroalkylgroup, n represents an integer of 0 to 3, the n atoms/groups of Y¹ maybe the same or different, Y² represents a fluorine or chlorine atom, mrepresents an integer of 1 to 5, the m atoms of Y² may be the same ordifferent, and A represents —SO₂X, —COOM³ _(1/L) or an organic groupcapable of undergoing hydrolysis and thus being converted to a carboxylgroup; X represents a halogen atom, —OM⁴ _(1/L), —NR¹³R¹⁴ or—ONR¹⁵R¹⁶R¹⁷R¹⁸ (wherein R¹³ and R¹⁴ are the same or different and eachrepresents a hydrogen atom, an alkali metal, an alkyl group or asulfonyl-containing group, M³ and M⁴ each represents a metal having avalence of L, and R¹⁵, R¹⁶, R¹⁷ and R¹⁸ are the same or different andeach represents a hydrogen atom or an alkyl group containing 1 to 4carbon atoms), or one derived from the fluoropolymer precursor mentionedabove.

When the crosslinkable fluoropolymer is such a fluoropolymer precursoras mentioned above, the groups —SO₂X (X is —OM⁴ _(1/L), —NR¹³R¹⁴ or—ONR¹⁵R¹⁶R¹⁷R¹⁸, M⁴ is as defined above and R¹³, R¹⁴, R¹⁵, R¹⁶, R¹⁷ andR¹⁸ are as defined above (—SO₂X corresponding to the acid/acid saltgroup)) and —COOM³ _(1/L) in the above general formula (II) are the sameas the acid/acid salt groups of the above-mentioned crosslinkablefluoropolymer.

The above-mentioned “one derived from the fluoropolymer precursor” isone obtained by hydrolyzing the fluoropolymer precursor in the presenceof water, as described later herein, or one obtained by interchangingthe alkali metal or the metal of valence L in the sulfonyl-containinggroup as represented by M³ or M⁴ or R¹³ and/or R¹⁴ in the generalformula (II), which the fluoropolymer precursor has, with another metalor cation or the like.

The fluorovinyl ether derivative mentioned above is represented by thegeneral formula (II) when n represents an integer of 0 to 3. The integern is preferably 0 or 1. The symbol m in the general formula (II)represents an integer of 1 to 5. The integer m is preferably 2.

The symbol Y¹ in the general formula (II) represents a fluorine orchlorine atom or a perfluoroalkyl group, and the n groups of Y¹ may bethe same or different. The perfluoroalkyl group is not particularlyrestricted but includes, among others, perfluoroalkyl groups containing1 to 3 carbon atoms, such as trifluoromethyl group and pentafluoroethylgroup.

The symbol Y² in the general formula (II) preferably represents afluorine or chlorine atom, and the m atoms of Y² may be the same ordifferent. In the general formula (II), Y¹ is preferably atrifluoromethyl group, and Y² is preferably a fluorine atom.

More preferably, the above fluorovinyl ether derivative is onerepresented by the general formula (II) wherein Y¹ is a trifluoromethylgroup, Y² is a fluorine atom, n is 0 or 1 and m is 2.

The fluoropolymer precursor mentioned above is preferably an at leastbinary copolymer obtained by polymerizing the above-mentionedfluorovinyl ether derivative and a fluoroethylenic monomer.

When the fluoropolymer precursor is such an at least binary copolymer,the composition ratio between the fluorovinyl ether derivative andfluoroethylenic monomer is preferably 1:99 to 50:50, more preferably5:95 to 30:70.

The fluoroethylenic monomer is not particularly restricted provided thatit contains a vinyl group. It is different from the fluorovinyl etherderivative mentioned above.

As the fluoroethylenic monomer, there may be mentioned, for example,haloethylenic monomers represented by the general formula:CF₂═CF-Rf¹wherein Rf¹ represents a fluorine or chlorine atom, -Rf² or —ORf² inwhich Rf² represents a straight or branched fluoroalkyl group containing1 to 9 carbon atoms which may optionally contain an ether oxygenatom(s), and hydrogen-containing fluoroethylenic monomers represented bythe general formula:CHY³═CFY⁴wherein Y³ represents a hydrogen or fluorine atom and Y⁴ represents ahydrogen, fluorine or chlorine atom, -Rf³ or —ORf³ in which Rf³represents a straight or branched fluoroalkyl group containing 1 to 9carbon atoms which may optionally contain an ether oxygen atom(s).

The fluoroethylenic monomer preferably comprises at least one selectedfrom the group consisting of CF₂═CF₂, CH₂═CF₂, CF₂═CFCl, CF₂═CFH,CH₂═CFH, CF₂═CFCF₃ and fluorovinyl ethers represented by CF₂═CF—O-Rf⁴(in which Rf⁴ represents a fluoroalkyl group containing 1 to 9 carbonatoms or a fluoropolyether group containing 1 to 9 carbon atoms. Thegroup Rf⁴ in the above fluorovinyl ether is preferably a perfluoroalkylgroup containing 1 to 3 carbon atoms.

The fluoroethylenic monomer is preferably a perhaloethylenic monomer, inparticular a perfluoroethylenic monomer, more preferably CF₂═CF₂.

As the fluoroethylenic monomer, one or two or more species can be used.

The above-mentioned crosslinkable fluoropolymer can be produced by anyof the known methods of polymerization, such as solution polymerization,emulsion polymerization and suspension polymerization.

The crosslinkable fluoropolymer may be a polymer produced by seededpolymerization.

When it is one containing sulfonic acid groups or carboxylic groups orthe above-mentioned sulfonic acid salt groups or carboxylic salt groups,the crosslinkable fluoropolymer is preferably one obtained byhydrolyzing the —SO₂X¹ (X¹ representing a halogen atom) or —COZ¹ (Z¹representing an alkoxyl group) group, which the fluoropolymer precursorhas, in the presence of water.

As the alkoxyl group in —COZ¹, there may be mentioned alkoxyl groupscontaining 1 to 4 carbon atoms, such as methoxy, ethoxy, propoxy andbutoxy groups. Among them, methoxy or ethoxy group is preferred.

The hydrolysis is carried out by adding an alkali, preferably an aqueoussolution of an alkali. As the alkali may be an alkali generally used forhydrolysis, for example, the hydroxide or carbonate of an alkali metalor alkaline earth metal. The hydroxide includes, among others, sodiumhydroxide, potassium hydroxide and lithium hydroxide, and the carbonateincludes sodium carbonate, sodium hydrogen carbonate and so forth.

The hydrolysis is generally carried out at ordinary temperature to 130°C. for 1 minute to 10 hours and, for example, when the acid/acid saltgroup precursor which the fluoropolymer precursor has is —SO₂F, thehydrolysis is generally carried out at 80° C. to 100° C. for 10 minutesto 5 hours.

The crosslinkable fluoropolymer contains crosslinkable functionalgroups.

The crosslinkable functional groups are groups consumed in thecrosslinking reaction. The “crosslinking” is the formation ofcrosslinkage bonds. As the crosslinkable functional groups, there may bementioned the above-mentioned acid/acid salt groups and acid/acid saltgroup precursors and, further, iodo [—I], bromo [—Br], cyano,crosslinkable carboxyl, cyanato, hydroxyl, perfluorovinyl andhalocarbonyl groups.

The above-mentioned acid/acid salt groups, organic groups capable ofundergoing hydrolysis and thus being converted to carboxyl groups, andacid/acid salt group precursors also include functional groups of thekind consumable in the crosslinking reaction. In the presentspecification, those functional groups of the kind consumable in thecrosslinking reaction which are actually consumed in the crosslinkingreaction are referred to as “crosslinkable functional groups” and thosewhich are not consumed in the crosslinking reaction are referred to as“acid/acid salt groups, organic groups capable of undergoing hydrolysisand thus being converted to carboxyl groups, and acid/acid salt groupprecursors” (hereinafter sometimes referred to as “non-crosslinkablefunctional groups”). The functional groups of the kind consumable in thecrosslinking reaction are, for example, carboxyl groups.

In the present specification, the “crosslinkable carboxyl groups” arecarboxyl groups consumed in the crosslinking reaction and, in thisrespect, are to be conceptually distinguished from those carboxyl groupswhich are not consumed in the crosslinking reaction but remain as theacid groups mentioned above even after the crosslinking treatment to bedescribed later herein. When the crosslinkable fluoropolymer in thepresent invention contains both carboxyl groups as acid groups andcrosslinkable carboxyl groups, both kinds of carboxyl groups generallyoccur in total in excess relative to the crosslinking agent (B), so thatthe carboxyl groups partly remain unconsumed in the crosslinkingreaction even in the crosslinking treatment described later herein andthe remaining carboxyl groups can function as the acid groups mentionedabove. In the present specification, those carboxyl groups which are tobe consumed in the crosslinking reaction are the above-mentionedcrosslinkable carboxyl groups, and those carboxyl groups remainingunconsumed in the crosslinking reaction are the carboxyl groups as acidgroups.

The above-mentioned crosslinkable fluoropolymer is preferably oneshowing an equivalent weight [EW] of 300 to 5000 after the crosslinkingreaction, although the equivalent weight may vary depending on thecrosslinking reaction conditions, among others. A more preferred lowerlimit to the EW after crosslinking reaction is 500, and a more preferredupper limit thereto is 1500. In the present specification, theequivalent weight [EW] after crosslinking reaction indicates the amountof the above-mentioned non-crosslinkable functional groups but does notindicate the amount of the crosslinkable functional groups.

The crosslinkable fluoropolymer is preferably one to be used as a resin,not as a rubber, after the crosslinking reaction.

The fluoropolymer liquid composition of the invention preferablycomprises the above-mentioned fluoropolymer liquid (A) and, further, acrosslinking agent (B), although this depends on the crosslinkablefunctional group species and the crosslinking system to be used.

When the crosslinkable functional groups are crosslinkable carboxyl,cyano, —I and/or —Br groups or moieties, for instance, the liquidcomposition can be cured without using the crosslinking agent (B). Whenthe crosslinkable functional groups are —I or —Br, curing is possiblewithout using the crosslinking agent (B) but curing may also be effectedusing the crosslinking agent (B).

As the curing agent (B), there may be mentioned those capable ofreacting with carboxyl, alkxoycarbonyl or cyano groups, in particularthose used in oxazole crosslinking systems, imidazole crosslinkingsystems and/or thiazole crosslinking systems. As the crosslinking agent(B) to be used in the oxazole crosslinking systems, imidazolecrosslinking systems and/or thiazole crosslinking systems, there may bementioned, for example, bisdiaminophenyl type crosslinking agents,bisaminophenol type crosslinking agents or bisaminothiophenol typecrosslinking agents represented by the general formula (IV):

wherein one of R¹⁹ and R²⁰ represents —NH₂ and the other represents—NH₂, —NH-Ph (Ph representing a phenyl group), —OH or —SH, R²¹represents —SO₂—, —O—, —CO—, an alkylene group containing 1 to 6 carbonatoms, a perfluoroalkylene group containing 1 to 10 carbon atoms or asingle bond, bisamidolazone type crosslinking agents represented by thegeneral formula (V):

wherein R²¹ is as defined above, R²⁶ represents

orand bisamidoxime type crosslinking agents represented by the generalformula (VI) or (VII):

wherein R_(f) ⁵ represents a perfluoroalkylene group containing 1 to 10carbon atoms;

wherein p represents an integer of 1 to 10. These bisaminophenol typecrosslinking agents, bisaminothiophenol type crosslinking agents orbisdiaminophenyl type crosslinking agents, among others, have so farbeen used in crosslinking systems in which nitrile groups serve ascrosslinking sites. However, they also react with the carboxyl groupsand alkoxycarbonyl groups in the fluoropolymer to form oxazole, thiazoleor imidazole rings and thus give crosslinked products.

As the crosslinking agent (B), there may also be mentioned compoundshaving a plurality of 3-amino-4-hydroxyphenyl groups and/or3-amino-4-mercaptophenyl groups, or crosslinking agents (B1) representedby the general formula (III):

wherein R¹⁹, R²⁰ and R²¹ are as defined above, for example2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (generic name:bis(aminophenol) AF),2,2-bis(3-amino-4-mercaptophenyl)hexafluoropropane, tetraaminobenzene,bis(3,4-diaminophenyl)methane, bis(3,4-diaminophenyl)ether and2,2-bis(3,4-diaminophenyl)hexafluoropropane.

As the crosslinking agent (B), there may further be mentioned polyaminecompounds, polyisocyanates, polyepoxidized compounds and the like. Thepolyamine compounds include, among others, polyamines such ashexamethylenediamine, triethylenetetramine and triethylenediamine; andcombinations of polyamine salts and guanidine derivatives. Thepolyisocyanate compounds include, for example, tolylene diisocyanate,diphenylmethanediisocyanate and hexamethylene diisocyanate. Thepolyisocyanate compounds may be in the form of prepolymers or in theblocked form making it possible to select the curing temperature. As thecrosslinking agent (B), there may further be mentioned, for example, thecombined use of an epoxy compound and a quaternary ammonium salt, aquaternary phosphonium salt or a basic compound.

When the above-mentioned crosslinkable functional groups are cyano orcrosslinkable carboxyl groups, the crosslinking agent (B) is preferablya crosslinking agent (B1) represented by the general formula (III) givenhereinabove.

The groups R¹⁹ and R²⁰ in the general formula (III) are preferably suchthat each is —NH₂ or one of them is —NH₂ and the other is —NH-Ph.

When the crosslinkable functional groups each is —I or —Br, thecrosslinking agent (B) is preferably a polyfunctional unsaturatedcompound.

The polyfunctional unsaturated compound is not particularly restrictedin kind but may be any one that is reactive with polymer radicals formedupon heating or due to iodine and/or bromine atoms generated upondecomposition of such peroxide compounds as mentioned later herein.Preferred polyfunctional unsaturated compounds are, for example, variousdiacrylates, trimethylolpropane triacrylate [TMTPA], trimethylolpropanetrimethacrylate, triallyl isocyanurate [TAIC], triallyl cyanurate,triallyl trimellitate, pentaerythritol triacrylate, pentaerythritoltetraacrylate, dipentaerythritol hexaacrylate,N,N′-m-phenylenebismaleimide, dipropargyl terephthalate, diallylphthalate, tetraallyl terephthalamide and triallyl phosphate. Amongthem, those containing three or more crosslinkable functional groups permolecule are preferred from the viewpoint of easy crosslinking of thecrosslinkable fluoropolymer, and triallyl isocyanurate is morepreferred.

The usage of the polyfunctional unsaturated compound is about 0.05 to 10parts by mass per 100 parts by mass of the crosslinkable fluoropolymer.A preferred lower limit thereto is 0.5 part by mass, and a preferredupper limit is 5 parts by mass.

In either of the case of the fluoropolymer liquid composition of theinvention occurring as a fluoropolymer solution (AS) and the case of itsoccurring as a fluoropolymer liquid dispersion (AD), which are to bedescribed later herein, the crosslinking agent (B) preferably amounts to0.05 to 20% by mass, more preferably to at least 0.1% by mass, relativeto the solid matter in the fluoropolymer liquid composition of theinvention.

The solid matter in the fluoropolymer liquid composition preferablyamounts to 0.5 to 50 parts by mass per 100 parts by mass of thefluoropolymer liquid composition.

The fluoropolymer liquid composition of the invention preferablycomprises the fluoropolymer liquid (A) and, further, at least onealcohol (C) selected from the group consisting of methanol, ethanol,propanol and tetrafluoropropanol.

Tetrafluoropropanol is more preferred as the alcohol (C), and2,2,3,3-tetrafluoropropanol is still more preferred. The alcohol (C) tobe used may comprise one single species or two or more species.

The level of addition of the alcohol (C) is preferably 10 to 80% byvolume relative to the fluoropolymer liquid (A). By adding the alcohol(C) in an amount within the above range, it becomes possible to adjustthe surface tension of the fluoropolymer liquid composition of theinvention and, thus, when the fluoropolymer liquid composition of theinvention is used for membrane molding, which is to be described laterherein, homogeneous membranes can be obtained.

The fluoropolymer liquid composition may comprise the fluoropolymerliquid (A), the alcohol (C) and, further, the above-mentionedcrosslinking agent (B).

The fluoropolymer liquid composition of the invention preferablycomprises the fluoropolymer liquid (A) and, further, a film-formingauxiliary agent (D). The addition of the film-forming auxiliary agent(D) produces marked improvements in film-forming ability and makes itpossible to produce thin membranes by casting.

The film-forming auxiliary agent (D) is preferably an organic liquidwhich is miscible with water and has a boiling point exceeding 100° C.but not exceeding than 300° C. When the boiling point is not higher than100° C., the boiling point is generally equal to or lower than that ofwater and, therefore, when a fluoropolymer liquid dispersion (AD) is tobe obtained by incorporating the film-forming auxiliary agent (D) to anfluoropolymer aqueous dispersion (ADA) comprising particles of acrosslinkable fluoropolymer (PD) dispersed in an aqueous dispersionmedium and then evaporating the moisture (conversion to an organosol),it is impossible to remove the aqueous dispersion medium while retainingthe film-forming auxiliary agent (D). When the boiling point is higherthan 300° C., the removal of the film-forming auxiliary agent (D) fromthe membrane formed using the fluoropolymer liquid composition obtained,if required, tends to become difficult. A preferred lower limit to theboiling point of the film-forming auxiliary agent (D) is 150° C., and apreferred upper limit thereto is 250° C.

When the fluoropolymer liquid (A) in the present invention is anfluoropolymer aqueous dispersion (ADA) or a fluoropolymer solution (AS)having, dissolved in an alcohol/water mixed solvent, a crosslinkablefluoropolymer, the use of the film-forming auxiliary agent (D) isparticularly preferred.

When the acid/acid salt group precursor is —SO₂NR²²R²³ (R²² and R²³being as defined above) or an organic group capable of undergoinghydrolysis and thus being converted to a carboxyl group except for thecases where the crosslinkable fluoropolymer (PS) in the fluoropolymerliquid (A) in the present invention has —SO₂F and occurs as afluoropolymer solution (AS) having the crosslinkable fluoropolymer (PS)dissolved in a fluorosolvent, the film-forming auxiliary agent (D)preferably comprises (1) a phosphate ester, (2) an ethylene oxideoligomer monohydroxy ether and/or (3) a cyclic amide or cyclic amidederivative.

The film-forming auxiliary agent (D) is preferably used in an amount of0.1 to 100 parts by mass per part by mass of the crosslinkablefluoropolymer. At levels lower than 0.1 part by mass, the film-formingability may be insufficient when the fluoropolymer liquid compositionobtained is used in molding membranes. At levels exceeding 100 parts bymass, the effect is no more proportional to the addition level and thisis economically unfavorable. A more preferred lower limit is 0.5 part bymass, and a more preferred upper limit is 20 parts by mass.

The above-mentioned fluoropolymer liquid composition may comprise thefluoropolymer liquid (A) and the film-forming auxiliary agent (D) and,further, the crosslinking agent (B), or may comprise the fluoropolymerliquid (A) and the crosslinking agent (B) and, further, the film-formingauxiliary agent (D) and the alcohol (C).

The fluoropolymer liquid composition may further also comprise thefluoropolymer liquid (A) and an active substance (E).

As the active substance (E), there may be mentioned, for example, thecatalyst described later herein referring to the method of producing afluorine-containing cured article according to the invention.

The fluoropolymer liquid composition may further comprise thefluoropolymer liquid (A), the active substance (E) and at least onespecies selected from the group consisting of the crosslinking agent(B), alcohol (C) and film-forming auxiliary agent (D).

The fluoropolymer liquid (A) is preferably a fluoropolymer liquiddispersion (AD), and the solid matter concentration of the fluoropolymerliquid dispersion (AD) is preferably 2 to 80% by mass. When thefluoropolymer liquid composition comprises the fluoropolymer liquiddispersion (AD) and further the crosslinking agent (B), as mentionedabove, the crosslinking agent (B) preferably amounts to 0.1 to 20% bymass of the solid matter in the fluoropolymer liquid composition.

The fluoropolymer liquid dispersion (AD) is preferably an fluoropolymeraqueous dispersion (ADA) in which the liquid dispersion medium is anaqueous dispersion medium, and the aqueous dispersion medium ispreferably has a water content of 10 to 100% by mass. When the watercontent of the aqueous dispersion medium is lower than 10% by mass, thedispersibility tends to unfavorably become poor. A more preferred lowerlimit is 40% by mass.

The “aqueous dispersion medium” so referred to herein is a dispersionmedium for the crosslinkable fluoropolymer (PD) and contains water. Theaqueous dispersion medium, which comprises water, may further contain awater-soluble organic solvent in addition to water. The aqueousdispersion medium may contain a surfactant, a stabilizer and/or anotheror other additives generally used in aqueous dispersions.

When the crosslinkable fluoropolymer has acid/acid salt groups, thefluoropolymer aqueous dispersion (ADA) has sufficient dispersionstability even if it is substantially free of any surfactant.

When the crosslinkable fluoropolymer is one obtained by emulsionpolymerization, the fluoropolymer aqueous dispersion (ADA) may be thedispersion obtained after polymerization as it is and, when thecrosslinkable fluoropolymer contained in the dispersion as obtainedafter polymerization is a fluoropolymer precursor having acid/acid saltgroup precursors, the fluoropolymer may be one obtained through theabove-mentioned hydrolysis.

The fluoropolymer aqueous dispersion (ADA) is preferably one purifiedfor the purpose of removing inorganic salts, low-molecular-weightimpurities, and polymers very low in molecular weight, among others. Asthe method of purification, there may be mentioned ultrafiltration, forinstance.

The fluoropolymer liquid dispersion (AD) may also be the so-calledorganosol obtained by evaporating the moisture after incorporation ofthe film-forming auxiliary agent (D) into the fluoropolymer aqueousdispersion (ADA).

The fluoropolymer liquid (A) may also be a fluoropolymer solution (AS),and the crosslinkable fluoropolymer (PS) preferably amounts to 0.1 to10% by mass of the fluoropolymer liquid composition. When thefluoropolymer liquid composition of the invention comprises thefluoropolymer liquid dispersion (AS) and further the crosslinking agent(B), as mentioned above, the crosslinking agent (B) preferably amountsto 0.1 to 20% by mass of the solid matter in the fluoropolymer liquidcomposition. When the crosslinkable fluoropolymer (PS) containsacid/acid salt group precursors, the liquid medium serving as a solventfor the crosslinkable polymer (PS) in the fluoropolymer solution (AS) ispreferably a fluorosolvent and, when it contains acid/acid salt groups,that liquid medium is preferably an alcohol/water mixed solvent.

The fluorosolvent contains fluorine atoms within the molecule and has aboiling point of 30 to 150° C. So long as it contains fluorine atomswithin the molecule and has a boiling point of 30 to 150° C., thefluorosolvent may be either aromatic or aliphatic.

The fluorosolvent is not particularly restricted but includes, amongothers, chlorofluorocarbons, perfluorobenzene and the like. Preferredamong others are linear chlorofluorocarbons represented by the generalformula (VIII):C_(a)H_(b)Cl_(c)F_((2a+2−b−c))   (VIII)wherein a is an integer of 3 to 6, b is an integer of 0 to 2 and c is aninteger of 0 to 4, or alicyclic chlorofluorocarbons represented by thegeneral formula (IX):C_(a)H_(b)Cl_(c)F_((2a−b−c))   (IX)wherein a, b and c are as defined above.

Preferred as the chlorofluorocarbons are those of the general formula(VIII) and general formula (IX) in which b is 0 or 1 and c is 1 or 2.More preferred are mixtures of CF₃CClFCClFCF₃ and CClF₂CClFCF₂CF₃, amixture [HCFC-225] of CF₃CF₂CHCl₂ and CClF₂CF₂CHClF, and H(CF₂CF₂)₂Cl.

Perfluorocyclobutane can also be used as the chlorofluorocarbon.

The alcohol to be used in the alcohol/water mixed solvent includes,among others, methanol, ethanol and isopropyl alcohol.

The mixing proportion of the alcohol in the alcohol/water mixed solventis preferably 10:90 to 90:10 (alcohol:water, % by volume).

The alcohol to be used in the alcohol/water mixed solvent may be thesame as the above-mentioned alcohol (C) for improving the film-formingability. However, said alcohol is essential for dissolving thecrosslinkable fluoropolymer (PS) and, in this respect, it is to beconceptually distinguished from the alcohol (C) which is not essential.

The dissolution treatment of the crosslinkable fluoropolymer (PS) in thefluoropolymer solution (AS) is carried out at a temperature not lowerthan the boiling point of the fluorosolvent or the alcohol/water mixedsolvent, preferably at 120° C. or above, more preferably 150° C. orabove. Therefore, the dissolution treatment is preferably carried out ina pressure vessel. The time for the dissolution treatment is generally10 minutes to 300 hours, although it may depend on the dissolutiontemperature.

The above-mentioned boiling point and dissolution treatment temperatureare the values at ordinary temperature and ordinary pressure. The term“ordinary temperature” as used herein indicates ordinary temperature inthe ordinary meaning of the term, generally 20-30° C., and the term“ordinary pressure” indicates ordinary pressure in the ordinary meaningof the term, generally 1013 hectopascals (=1 atm.).

The fluoropolymer liquid composition of the invention can be prepared byadding the crosslinking agent (B) after cooling, to ordinary temperatureonce, the fluoropolymer liquid dispersion (AD) or fluoropolymer solution(AS) prepared with heating. When the fluoropolymer liquid composition ofthe invention is prepared according to such procedure, there will neverarise the problem caused by the addition of the crosslinking agent (B)on the occasion of heating, namely the problem of premature progress ofthe crosslinking reaction, with the consequent failure to provide thedesired fluoropolymer liquid composition.

The fluoropolymer liquid composition of the invention can be suitablyused as a proton-conductive material, in particular as aproton-conductive membrane material.

In the method of producing a fluorine-containing cured article accordingto the invention, such a cured article is produced by applying thefluoropolymer liquid composition of the invention to a substrate orimpregnating a porous material with that composition, removing theliquid medium and then carrying out the crosslinking treatment.

The fluorine-containing cured article mentioned above can be oneimproved in mechanical characteristics, reduced in dimensional changesdue to the moisture content and, as a result, improved in durability ascompared with the membrane obtained by applying the fluoropolymer liquidcomposition mentioned above to the substrate or impregnating the porousmaterial with that composition and removing the liquid medium withoutcarrying out the crosslinking treatment.

The method of producing a fluorine-containing cured article according tothe invention can generally produce the fluorine-containing curedarticle in an industrially efficient and stable manner by using thefluoropolymer liquid composition of the invention.

The substrate mentioned above is not particularly restricted butincludes, among others, the porous support mentioned above, resinmoldings, and metal plates. Electrolyte membranes and porous carbonelectrodes, which are used in fuel cells and the like, and the like arepreferred.

The above-mentioned porous material may be any organic or inorganicmaterial having a porous structure. Thus, mention may be made of, forexample, glass wool, ceramics, alumina, polytetrafluoroethylene webs,stretched porous films obtained by molding polytetrafluoroethylene,carbon, and various polymer-made articles.

Generally, the liquid medium mentioned above can be removed by drying atordinary temperature and/or with heating. The drying of the membraneobtained by applying the fluoropolymer liquid composition to a substrateor impregnating a porous material with that composition is preferablycarried out at least with heating, since when the drying is carried outat ordinary temperature alone, the membrane may be readily dissolved inwater or the like. The “heating” in removing the liquid medium isgenerally carried out at 80 to 400° C., preferably at 200° C. or above.

The fluorine-containing cured article may comprise a substrate or porousmaterial. When it is applied to a substrate, it can be obtained in theform of a substrate-free thin membrane by peeling it off from thesubstrate surface, for example by immersion in water.

The crosslinking treatment preferably consists in crosslinking treatmentusing high energy.

The crosslinking treatment using high energy is preferably carried outby heating, radiation exposure, electron beam irradiation orphotoirradiation. Preferably, the treatment is carried out by heating inview of the ready availability of the apparatus and the ease ofhandling.

The heating in the above crosslinking treatment is generally carried outin an oven or under pressing at 100 to 400° C. for 1 minute to 10 hours.

When the crosslinking treatment is carried out using a peroxidecompound, which is to be described later herein, as a crosslinkingreaction initiator, the treatment is preferably carried out in thesubstantial absence of oxygen, more preferably in a nitrogen atmosphere.In the presence of oxygen, the radicals generated upon cleavage of theperoxide compound are captured by oxygen and the progress of thecrosslinking tends to be prevented accordingly.

The method of producing a fluorine-containing cured article according tothe invention may also comprise applying the fluoropolymer liquidcomposition of the invention to a substrate or impregnating a porousmaterial with that composition, removing the liquid medium and carryingout the crosslinking treatment using a peroxide compound as acrosslinking reaction initiator to thereby produce a fluorine-containingcured article.

When the crosslinking treatment is carried out using a peroxide compoundas a crosslinking reaction initiator, the fluoropolymer liquidcomposition is preferably one in which the crosslinkable functionalgroup is —I or —Br and a polyfunctional unsaturated compound is used asthe crosslinking agent (B). Triallyl isocyanurate is preferred as thepolyfunctional unsaturated compound.

The peroxide compound is preferably one showing an appropriate rate ofdecomposition at a temperature not lower than the boiling point of theliquid medium but not higher than the decomposition temperature of thecrosslinkable fluoropolymer and having an evaporation temperature suchthat it will not easily evaporate and, as such, there may be mentioneddi-tert-butylperoxyalkanes, for example2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

The level of addition of the peroxide compound is preferably 0.001 to 5parts by mass per 100 parts by mass of the fluoropolymer. At levelsbelow 0.001 part by mass per 100 parts by mass of the fluoropolymer, thecrosslinking reaction may proceed only to an insufficient extent. Atlevels exceeding 5 parts by mass per 100 parts by mass of thefluoropolymer, the amount of the peroxide residues becomes great,possibly leading to a decrease in strength. A more preferred lower limitto the level of addition of the peroxide compound is 0.01 part by mass,and a more preferred upper limit thereto is 1 part by mass, per 100parts by mass of the fluoropolymer.

It is desirable that the above-mentioned application or impregnation becarried out at a relatively low temperature and then the crosslinkingtreatment be carried out by raising the temperature. The application orimpregnation and the crosslinking treatment may be repeated alternately.

The fluorine-containing cured article can be used, for example, as aproton-conductive membrane, in particular an electrolyte membrane or anion exchange membrane, without any particular restriction.

When the fluorine-containing cured article mentioned above is used as anelectrolyte membrane, for instance, it may have a membrane thickness of5 to 200 μm. A preferred lower limit to the above membrane thickness is10 μm, and a preferred upper limit to the membrane thickness is 50 μm.

When used as an electrolyte membrane, for instance, thefluorine-containing cured article mentioned above shows only a lowmembrane expansion rate even after a long period of immersion. Forexample, a fluorine-containing cured article obtained by crosslinking acrosslinkable fluoropolymer having a perfluoro(ethyl vinylether)sulfonyl chloride monomer unit content of 18 mole percent, whenimmersed in an aqueous medium for about 15 hours, the percentage ofmembrane expansion is generally not higher than 10% by volume ascompared with the volume before that immersion.

The fluorine-containing cured article mentioned above can be used,without any particular restriction, as an electrolyte membrane in asolid polymer electrolyte fuel cell, a membrane in a lithium cell, amembrane for electrolysis of sodium chloride, a membrane forelectrolysis of water, a membrane for electrolysis of a hydrohalic acid,a membrane in an oxygen concentrator, a membrane in a humidity sensor,or a membrane for a gas sensor, for instance.

The fluorine-containing cured article obtained by the method ofproducing a fluorine-containing cured article according to the inventionmay be an immobilized active substance cured article containing anactive substance (E).

The active substance/material (E) is not particularly restricted but maybe any one capable of showing its activity in the immobilized activesubstance cured article. It can be adequately selected according to theintended object of the immobilized active substance cured article of theinvention. For example, a catalyst can be suitably used.

The catalyst is not particularly restricted but may be any of thosegenerally used as electrode catalysts. For example, there may bementioned metals containing platinum, ruthenium or the like; and organicmetal complexes generally containing one or more central metal speciesin which at least one of the central metal species is platinum orruthenium. The platinum- or ruthenium-containing metals are preferablyplatinum-containing metals, although they may also beruthenium-containing metals, for example ruthenium as a simplesubstance. The platinum-containing metals are not particularlyrestricted but include, among others, platinum as a simple substance(platinum black); and platinum-ruthenium alloys. The catalyst isgenerally used in a form carried on a support such as silica, alumina orcarbon.

The immobilized active substance cured article mentioned above mayfurther comprise electrodes and/or other constituents constituting asolid polymer electrolyte fuel cell, and preferably is an electrode bodyfor a solid polymer electrolyte fuel cell.

The fluorine-containing cured article mentioned above can be used in theform of a membrane electrode assembly (MEA) which is an electrode bodyfor a solid polymer electrolyte fuel cell joining together with anelectrolyte membrane.

Effects of the Invention

The fluoropolymer liquid composition of the invention, which has theconstitution described hereinabove, can produce cured articles excellentin mechanical characteristics and durability and undergoing only slightdimensional changes depending on the moisture content in an industriallyefficient and stable manner.

BEST MODES FOR CARRYING OUT THE INVENTION

The following examples illustrate the present invention morespecifically. These examples are, however, by no means limitative of thescope of the present invention.

EXAMPLE 1

A 500-ml SUS stainless steel autoclave was charged with 227.5 g ofperfluorocyclobutane as a solvent, 168.2 g of perfluoro(ethyl vinylether)sulfonyl fluoride (PFSF, CF₂═CFOCF₂CF₂SO₂F) and 16.1 g ofCF₂═CFOCF₂CF(CF₃)OCF₂CF₂CN (CNVE), followed by deaeration. With stirringat 800 rpm and under the temperature condition of 30° C.,tetrafluoroethylene [TFE] was introduced under pressure to a totalpressure of 0.33 MPa and, then, 3.56 g of a 8% (by mass) solution of theinitiator di(ω-hydroperfluorohexanoyl)peroxide in perfluorohexane wasfed under pressure to initiate the polymerization reaction. Duringreaction, TFE was introduced from outside the system to maintain thepressure at constant level, and PFSF was introduced intermittently underpressure, in a total amount of 7.0 g, to compensate the PFSF consumptionin the reaction. After the lapse of 2 hours, the unreacted TFE wasdischarged out of the system to thereby terminate the polymerizationreaction. The state of stirring in the system was good. After completionof the polymerization reaction, 250 ml of chloroform was added, and theresulting mixture was stirred for 30 minutes. Then, using a centrifuge,solid-liquid separation was effected, 250 ml of chloroform was added tothe solid obtained, and the mixture was stirred for 30 minutes. Thepolymer was washed by repeating this procedure three times. Then, thewashed polymer was deprived of the chloroform under vacuum at 120° C.,to give 21.8 of a copolymer (copolymer a). The copolymer a obtained hada PFSF content of 16.2 mole percent and a CNVE content of 1.1 molepercent, as estimated from NMR spectrometry in a molten state at 300° C.

H(CF₂)₄Cl (400 ml) was added, as a fluorosolvent, to 4 g of thecopolymer a obtained and the whole was introduced into a 600-ml SUSstainless steel pressure vessel. After maintaining at 150° C. for 12hours, the contents were taken out, whereby a colorless transparentsolution was obtained. A 32-mg portion of2,2-bis[3-amino-4-(N-phenylamino)phenyl]hexafluoropropane (AFTA-Ph), acrosslinking agent synthesized by the method described in Journal ofPolymer Science, Polymer Chemistry Edition, Vol. 20, pages 2381-2393(1982), was admixed with the solution obtained. Apolytetrafluoroethylene [PTFE] porous membrane (product of DaikinIndustries) was immersed in the solution obtained, then air-dried for 30minutes, and dried in an oven set at 80 to 100° C. for 30 minutes. Then,the thus-formed coated membrane was further baked at 200° C. for 10minutes, then immersed in pure water and the thin membrane was peeledoff from the supporting glass plate. The thin membrane obtained had amembrane thickness of 15 μm.

EXAMPLE 2

An ice-cooled 300-ml autoclave equipped with a stirrer was charged with150 ml of pure water, 3 g of ammonium perfluorooctanoate, 37 g ofperfluoro(ethyl vinyl ether)sulfonyl fluoride (PFSF, CF₂═CFOCF₂CF₂SO₂F),0.18 g of I(CF₂)₄I and 60 mg of ammonium persulfate and, aftersufficient substitution of the inside space with tetrafluoroethylene[TFE], the inside was pressurized to 0.2 MPa with TFE, the system insidetemperature was rapidly raised to 60° C., and TFE was additionally feduntil arrival at a pressure of 0.8 MPa to thereby initiate thepolymerization. The reaction was continued while additionally feedingTFE to compensate the decrease in pressure and maintain the pressure at0.8 to 0.75 MPa. After the lapse of 6 hours, the autoclave was rapidlycooled to 20° C. or below and the unreacted TFE was released; thepolymerization was thus stopped. A slightly turbid, transparentfluoropolymer aqueous dispersion (240 g) was obtained.

A portion of the fluoropolymer aqueous dispersion (BDA-1) obtained wascoagulated with nitric acid, and the solid was washed with water anddried. The thus-obtained crosslinkable fluoropolymer had an iodinecontent of 0.1% and had a PFSF content of 18.5 mole percent as estimatedfrom NMR spectrometry in a molten state at 300° C.

A 50-ml portion of the fluoropolymer aqueous dispersion obtained wasdiluted two-fold with pure water, the dilution was stirred in a 200-mlbeaker, the temperature was raised to 55° C., and the —SO₂F moietieswhich the fluoropolymer precursor had were hydrolyzed while maintainingthe pH at 10 or above by adding dropwise a 10% (by mass) aqueoussolution of potassium hydroxide. After about 3 hours, the pH no morelowered. However, the hydrolysis procedure was continued for further 2hours and then finished. During the procedure, no fluoropolymerdeposition was confirmed by the eye. The reaction mixture obtained wasdeprived of low-molecular-weight substances and purified andconcentrated by centrifugal ultracentrifugation using Centriprep YM-10(product of Amicon). The fluoropolymer dispersion obtained had afluoropolymer concentration of 32% by mass. In 10 ml of thefluoropolymer aqueous dispersion obtained, there were incorporated, withstirring, 12 ml of triethyl phosphate, 5 ml of isopropanol, 50 mg ofPerhexa 25B (product of NOF Corp.) and 150 mg of triallyl isocyanurate(TAIC) (product of Nippon Kasei Chemical). The thus-obtainedfluoropolymer dispersion composition was spread on a glass sheet and,after 30 minutes of air-drying, dried in an oven set at 80° C. for 30minutes, to give a coat film. Then, the glass sheet with the coat filmwas sealed with an aluminum foil and baked at 170° C. for 10 minutes.After cooling, the glass sheet with the coat film was taken out of thealuminum foil and immersed in pure water, the thin membrane was peeledoff from the glass sheet, immediately taken out of the water andair-dried at room temperature. The thin membrane had a thickness of 15μm. The thin membrane obtained was immersed in pure water at roomtemperature for 15 hours, whereupon it showed a percentage of membraneexpansion (volume ratio) of not higher than 10%.

COMPARATIVE EXAMPLE 1

The procedure of Example 2 was followed in the same manner except thatthe use of Perhexa 25B and TAIC was omitted. The membrane obtainedshowed a percentage of membrane expansion of 20%.

EXAMPLE 3

The procedure of Example 2 was followed in the same manner except thatthe amount of perfluoro(ethyl vinyl ether)sulfonyl fluoride (PFSF,CF₂═CFOCF₂CF₂SO₂F) was increased to 49 g. The PFSF content estimatedfrom NMR spectrometry in a molten state at 300° C. was 23.4 molepercent, and the percentage of membrane expansion was 160%.

COMPARATIVE EXAMPLE 2

The procedure of Example 3 was followed in the same manner except thatthe use of Perhexa 25B and TAIC was omitted. The thin membrane obtained,when immersed in pure water at room temperature for 15 hours, wasdissolved in water.

EXAMPLE 4

The same autoclave as used in Example 3 was charged with 50 ml of thefluoropolymer dispersion obtained in Example 3 after removal oflow-molecular-weight substances and purification and concentration bycentrifugal ultrafiltration, 100 ml of pure water and 20 mg of ammoniumpersulfate and, after sufficiently purging the reaction vessel withhexafluoropropylene [HFP] gas, the pressure was increased to 1 MPa with20 g of HFP gas and TFE at 4° C., and the temperature was then raised to60° C. to initiate the block polymerization for the production of aTFE/HFP copolymer. After the pressure drop from 1.6 MPa at the initialto 1.1 MPa in 5 hours, the temperature was lowered to 20° C. or below,and the pressure was released to give 165 ml of an fluoropolymer aqueousdispersion. The reaction mixture obtained was further subjected tocentrifugal ultrafiltration using Centriprep YM-10 (product of Amicon)for the removal of low-molecular-weight substances and purification andconcentration of the fluoropolymer. In 10 ml of the fluoropolymeraqueous dispersion obtained, there were incorporated, with stirring, 12ml of triethyl phosphate, 5 ml of isopropanol, 50 mg of Perhexa 25B(product of NOF Corp.) and 150 mg of triallyl isocyanurate (TAIC)(product of Nippon Kasei Chemical). The thus-obtained fluoropolymerdispersion composition was spread on a glass sheet and, after 30 minutesof air-drying, dried in an oven set at 80° C. for 30 minutes, to give acoat film. Then, the glass sheet with the coat film was sealed with analuminum foil and baked at 170° C. for 10 minutes, followed by further 5minutes of heating at 295° C. After cooling, the glass sheet with thecoat film was taken out of the aluminum foil and immersed in pure water,the thin membrane was peeled off from the glass sheet, immediately takenout of the water and air-dried at room temperature. The thin membranehad a thickness of 15 μm. The thin membrane obtained was immersed inpure water at room temperature for 15 hours; the percentage of membraneexpansion was 0%. The ion exchange capacity of the membrane obtained wasdetermined by titrimetry and found to be 870 g/equivalent.

EXAMPLE 5

The procedure of Example 3 was followed in the same manner except that 2g of CF₂═CFOCF₂CF₂I was used in lieu of I(CF₂)₄I. The PFSF contentestimated from NMR spectrometry in molten state at 300° C. was 23.0 molepercent, and the percentage of membrane expansion was 5%.

INDUSTRIAL APPLICABILITY

The fluoropolymer liquid composition of the invention can be suitablyused in the production of electrolyte membranes, among others.

1. A fluoropolymer liquid composition comprising a fluoropolymer liquid(A) which comprises a liquid medium and a crosslinkable functionalgroup-containing crosslinkable fluoropolymer, wherein said fluoropolymerliquid (A) is a fluoropolymer liquid dispersion (AD) having, dispersedin a liquid dispersion medium, particles of a crosslinkablefluoropolymer (PD) containing acid/acid salt groups or organic groupscapable of undergoing hydrolysis and thus being converted to carboxylgroups, or a fluoropolymer solution (AS) having, dissolved in afluorosolvent or an alcohol/water mixed solvent, a crosslinkablefluoropolymer (PS) containing acid/acid salt groups or acid/acid saltgroups precursors; said acid/acid salt groups are sulfonic acid groups,carboxyl groups or groups of the formula —SO₂NR²R³, —SO₃NR⁴R⁵R⁶R⁷,—SO₃M¹ _(1/L), —COONR⁸R⁹R¹⁰R¹¹ or —COOM² _(1/L), wherein R² represents ahydrogen atom or M⁵ _(1/L), R³ represents an alkyl group or ansulfonyl-containing group, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰ and R¹¹ are thesame or different and each represents a hydrogen atom or an alkyl group,and M¹, M² and M⁵ each represents a metal having a valence of L, saidmetal having a valence of L being a metal belonging to the group 1, 2,4, 8, 11, 12 or 13 of the periodic table; and said acid/acid salt groupsprecursors are —SO₂F, —SO₂NR²²R²³ (wherein R²² and R²³ are the same ordifferent and each represents an alkyl group) or organic groups capableof undergoing hydrolysis and thus being converted to carboxyl groups. 2.The fluoropolymer liquid composition according to claim 1, wherein saidacid/acid salt groups, said acid/acid salt groups precursors, and saidorganic groups capable of undergoing hydrolysis and thus being convertedto carboxyl groups are each bound to a fluoroether side chainrepresented by the general formula (I):—O—(CF₂CFY¹—O)_(n)—(CFY²)_(m)—  (I) wherein Y¹ represents a fluorine orchlorine atom or a perfluoroalkyl group, n represents an integer of 0 to3, the n atoms/groups of Y¹ may be the same or different, Y² representsa fluorine or chlorine atom, m represents an integer of 1 to 5, and them atoms of Y² may be the same or different; and wherein said fluoroetherside chain is bound, via ether bonding, to a carbon atom constituting aperfluoroethylene unit in the main chain of the crosslinkablefluoropolymer.
 3. The fluoropolymer liquid composition according toclaim 1, wherein said crosslinkable fluoropolymer is a fluoropolymerprecursor obtained by polymerizing a fluorovinyl ether derivativerepresented by the general formula (II):CF₂═CF—O—(CF₂CFY¹—O)_(n)—(CFY²)_(m)-A   (II) wherein Y¹ represents afluorine or chlorine atom or a perfluoroalkyl group, n represents aninteger of 0 to 3, the n atoms/groups of Y¹ may be the same ordifferent, Y² represents a fluorine or chlorine atom, m represents aninteger of 1 to 5, the m atoms of Y² may be the same or different, and Arepresents —SO₂X, —COOM³ _(1/L) or an organic group capable ofundergoing hydrolysis and thus being converted to a carboxyl group; Xrepresents a halogen atom, —OM⁴ _(1/L), —NR¹³R¹⁴ or —ONR¹⁵R¹⁶R¹⁷R¹⁸,wherein R¹³ and R¹⁴ are the same or different and each represents ahydrogen atom, an alkali metal, an alkyl group or a sulfonyl-containinggroup, M³ and M⁴ each represents a metal having a valence of L, and R¹⁵,R¹⁶, R¹⁷ and R¹⁸ are the same or different and each represents ahydrogen atom or an alkyl group containing 1 to 4 carbon atoms, or onederived from said fluoropolymer precursor.
 4. The fluoropolymer liquidcomposition according to claim 3, wherein said fluoropolymer precursoris an at least binary copolymer obtained by polymerization of saidfluorovinyl ether derivative and a fluoroethylenic monomer.
 5. Thefluoropolymer liquid composition according to claim 3 4, wherein Y¹ is atrifluoromethyl group, Y² is a fluorine atom, n is 0 or 1, and m is 2.6. The fluoropolymer liquid composition according to claim 1, whereinthe organic groups capable of undergoing hydrolysis and thus beingconverted to carboxyl groups are —COOR¹², in which R¹² represents analkyl group, or —CONR²⁴R²⁵, in which R²⁴ and R²⁵ are the same ordifferent and each represents an alkyl group or a hydrogen atom.
 7. Thefluoropolymer liquid composition according to claim 1, wherein thecrosslinkable functional group is a cyano group or a crosslinkablecarboxyl group and wherein said fluoropolymer liquid compositioncomprises the fluoropolymer liquid (A) and, further, a crosslinkingagent (B), said crosslinking agent (B) being a crosslinking agent (B1)represented by the general formula (III):

wherein one of R¹⁹ and R²⁰ represents —NH₂ and the other represents—NH₂, —NH-Ph, —OH or —SH, Ph represents phenyl group and R₂₁ represents—SO₂—, —O—, —CO—, an alkylene group containing 1 to 6 carbon atoms, aperfluoroalkylene group containing 1 to 10 carbon atoms or a singlebond.
 8. The fluoropolymer liquid composition according to claim 7,wherein R¹⁹ and R²⁰ each is —NH₂ or one of them is —NH₂ and the other is—NH-Ph.
 9. The fluoropolymer liquid composition according to claim 1,wherein the crosslinkable functional group is —I or —Br, wherein saidfluoropolymer liquid composition comprises the fluoropolymer liquid (A)and, further, a crosslinking agent (B), said crosslinking agent (B)being a polyfunctional unsaturated compound.
 10. The fluoropolymerliquid composition according to claim 9, wherein the polyfunctionalunsaturated compound is triallyl isocyanurate.
 11. The fluoropolymerliquid composition according to claim 1, said fluoropolymer liquidcomposition comprising the fluoropolymer liquid (A) and, further, atleast one alcohol (C) selected from the group consisting of methanol,ethanol, propanol and tetrafluoropropanol.
 12. The fluoropolymer liquidcomposition according to claim 1, said fluoropolymer liquid compositioncomprising the fluoropolymer liquid (A) and, further, a film-formingauxiliary agent (D), said film-forming auxiliary agent (D) being anorganic liquid miscible with water and having a boiling point exceeding100° C. but not exceeding 300° C.
 13. The fluoropolymer liquidcomposition according to claim 12, wherein the acid/acid salt groupsprecursors each is —SO₂NR²²R²³ or a group capable of undergoinghydrolysis and thus being converted to a carboxyl group, R²² and R²³being as defined above and wherein the film-forming auxiliary agent (D)is (1) a phosphate ester, (2) an ethylene oxide oligomer monohydroxyether and/or a cyclic amide or a cyclic amide derivative.
 14. Thefluoropolymer liquid composition according to claim 1, saidfluoropolymer liquid composition comprising the fluoropolymer liquid (A)and, further, an active substance (E).
 15. The fluoropolymer liquidcomposition according to claim 1, wherein said crosslinkablefluoropolymer contains sulfonic acid groups or carboxyl groups, or saltforms of sulfonic acid groups or carboxyl groups, said crosslinkablefluoropolymer is obtained by hydrolysis, in the presence of water, ofgroups of the formula —SO₂X¹ or —COZ¹ contained in the fluoropolymerprecursor, X¹ representing a halogen atom and Z¹ representing an alkoxylgroup.
 16. The fluoropolymer liquid composition according to claim 1,wherein the fluoropolymer liquid (A) is a fluoropolymer liquiddispersion (AD) and wherein the solid matter concentration of saidfluoropolymer liquid dispersion (AD) is 2 to 80% by mass.
 17. Thefluoropolymer liquid composition according to claim 16, thefluoropolymer liquid dispersion (AD) being an fluoropolymer aqueousdispersion (ADA) in which the liquid dispersion medium is an aqueousdispersion medium, said aqueous dispersion medium having a water contentof 10 to 100% by mass.
 18. The fluoropolymer liquid compositionaccording to claim 1, wherein the fluoropolymer liquid (A) is afluoropolymer solution (AS) and wherein the crosslinkable fluoropolymer(PS) amounts to 0.1 to 10% by mass of said fluoropolymer liquidcomposition.
 19. A method of producing a fluorine-containing curedarticle, in which the fluoropolymer liquid composition according toclaim 1 is applied to a substrate or a porous material is immersed insaid composition, the liquid medium is then removed and a crosslinkingtreatment is carried out to produce said fluorine-containing curedarticle.
 20. A method of producing a fluorine-containing cured article,in which the fluoropolymer liquid composition according to claim 9 isapplied to a substrate or a porous material is immersed in saidcomposition, the liquid medium is then removed and a crosslinkingtreatment is carried out using a peroxide compound as a crosslinkingreaction initiator to produce said fluorine-containing cured article.21. The method of producing a fluorine-containing cured articleaccording to claim 19, wherein the crosslinking treatment is acrosslinking treatment using high energy.
 22. The method of producing afluorine-containing cured article according to claim 21, wherein thecrosslinking treatment using high energy is carried out by heating,exposure to radiation, electron beam irradiation or photoirradiation.23. The method of producing a fluorine-containing cured articleaccording to claim 19, wherein said fluorine-containing cured articlecomprises an immobilized active substance cured article containing anactive substance (E).
 24. The method of producing a fluorine-containingcured article according to claim 23, wherein the active substance (E) isa catalyst.
 25. The method of producing a fluorine-containing curedarticle according to claim 24, wherein the catalyst is aplatinum-containing metal.
 26. The method of producing afluorine-containing cured article according to claim 23, wherein theimmobilized active substance cured article is an electrode body for asolid polymer electrolyte fuel cell.
 27. The method of producing afluorine-containing cured article according to claim 19, wherein saidfluorine-containing cured article is an electrolyte membrane.
 28. Themethod of producing a fluorine-containing cured article according toclaim 23, wherein said fluorine-containing cured article is a membraneelectrode assembly (MEA) which is the electrode body for a solid polymerelectrolyte fuel cell joining together with the electrolyte membrane.